Automatic ringing-circuit and apparatus for telephone-exchanges



1 v R. H. MANSON. AUTOMATIC RINGING CIRCUIT AND APPARATUS FOR TELEPHONE EXCHANGES.

AEPLIOA'I'ION FILED P33. 1, 1907.

Patented July 6, 1909.

, e samura -sum 1.

R. H. MANSON. AUTOMATIC BINGING CIRCUIT AND APPARATUS FGB TELEPHONE EXCHANGES.

APPLICATION FILED FEB. 1, 1907.

Patented July 6, 1909.

'6 SHEETS-SHEET 2,

Suva-x for,

J 3 B 1 I t.

attorney Rn H. MANSON. AUTOMATIC RINGING CIRCUIT AND APPARATUS FOR TELEPHONE EXGHANGESL APPLICATION FILED FEB. 1, 1507. 9265950, Patented July 6, 1909.

6 SHEETS-SHEET 3.

Eli wen l'oz R. H. MANSON. AUTOMATIG RINGING CIRCUIT AND APPARATUS FOR TELEPHONE EXCHANGES.

I APPLIGATIOK FILED FEB. 1, 1907. 926,950, Patented July 6, 19097 6 SHEETS-SE33?) 4 Window v B. H. MANSON. AUTOMATIC RINGING GIRQUIT AND APPARATUS FOR TELEPHONE EXCHANGES.

APPLICATION FILED FEB. 1, 1907A Patented July 6, 1909.

6 SHEETS-SHEET 54.

Wc'lneaa ea.-

R. HQMANSON.

AUTOMATIC RINGING GIRGUI'I AND APPARATUS FOR TELEPHONE EXCHANGES APPLICATION FILED FEB. II 1907.

926,950. Patented July 6,1909.

QSHEETS-SHEET 6.

minim hm cwm NITED sTArns PATENT OFFICE RAY. n. anson, or ELYRIA, onro, ASSIGNOR TO THEDEAN ELECTRIGCOMPANY, or EIIJYRIA,

onio, A CORPORATION OF onto.

AUTOMATIC R ueme-omcurr AND APPARATUS jnoRi'rELErHouE-ExcHANGEs.

" 'N'b. 926,950. i

To all whom it may concern: Be it known that I, RAY H. MANSON, a citi- "zen-of' the United States, residing at Elyria,

in the county of Lorain and State of Ohio,

have invented certain new and useful Improvements in Automatic Ringing-Circuits Myinvention relates to telephone exchange.

systems, and has for its object the production of a ringing circuit for such systems. which shall be automatically controlled by the joint act of the operator and the called subscriber,

the formerconnectingthe ringin enerator to the called line, and the subscribgr discon necting when he answers the call. In this circuit I em loya thermal type-of relay for cutting off t 1e ringing current and commuta-.

tors for interrupting the flow ofgenerator current so as to give intermittent ringing.

These interrupter commutators are so arranged as to provide a ground or shunt path H place of the generator when ringing so that the release relay will'be operated as soon as the telephone receiver is removed from the switch hook at the called station.

' In designing the present circuit I have founditnecessary, in order to use a thermal or hot wire relay, to provide a shunt path for line current'around the same, to equalize the effects of the alternating ringing current and F the direct battery current, so that the thermal relay will operate the same when either current is passingthrough its wire." For this purpose I preferably em why a condenser, and I have found that sue 1 a condenser will act automatically as an equalizer for the different frequencies employed in harmonic party line signaling so as to produce a uniform operation of the thermal relay regardless of the character of thercurrent.

- My invention is illustrated in-the accompanying drawings in which Flgure 1 is a diagram of a central oificc cord circuit and two subscribers lines adapt- .ed to be connected thereby. Figs. 2 and 3 are diagrams of modified substation circuits. Fig. 41s a diagram of a modified cord circuit. F g. 5 IS a diagram similar to Fig. 1, showing the. calling end of a cordcircuit with a multigenerator equipment and connectlons for harmonic ringing, anda subscribers party line having harmonic ringers. Fig. 6 is a dial Specification or Letters Patent.

Application,filed February 1, 1907; Serial No. 356,208.

ply circuit.

Patented July 6,, 1909:

gram showing a cut-off type of key h aving a special arrangement. to prevent two keys from being depressed'at once and thereby connecting current-of two frequencies to the ringing circuit. Fig. 7 is adiagram showing aselective key havin a master contact for setting the ringing re ay. The contacts on this key are in parallel. FigfiS is a diagram of a modification of the same keyshowing cut-off contactsto prevent ciossing of two frequencies. adapted for use 1n the circuits shown. Fig. 10 is an end view of said key. Fig. 11 is a modified detailview of a-portion of Fig. 1;

Fig. 12 is amodified detail view of a portion of Fig.- 5..

Referring to the drawings, and particularly to Fig. 1, A and A are two subscribers? stations each equippedw-ith the apparatus usually employed in common battery systems. As the line and other connections and apparatus of thesetv/o sub-stations are identical, one description will suifice for both. The line wires 1'2 from station A pass to the central office, where they terminate upon a jack J and at the contacts of a cut-ofi relay N, through which they are normally connected to the-line relay M and'the main battery B on one side, and to the ground on the other. Relay M controls the line signal lamp m. The relay N has its windings connected on one side to the ground and on the other-side through a wire 3 to the'test thiinble. or ring 7' of the jack J Of coursein the case of a multiple board the springsfy' and j and the Fig. 9 is a side view of a key thimble j will all be duplicated 'and connected in multiple to the wires 1%2 For the purpose of interconnecting the lines, I provide the usual plugs P and P connected by the cord circuits 45- and 67. The

Y cord circuit is provided with supervisory roilays R-R and R R controlling the supervisory lamps rr The main battery B is bridged across each end of the cord be-- tween the tip and sleeve relays, in the usual manner, these relays tl161( -8 serving as impedance or choking coils in the battery supof testing lines to ascertain if they are busy, I provide the usual operators telephone set, with a suitable key for connecting it across the cord conductors 4.6, and test contacts controlled by the relay R For the purpose of ringing the wanted subscriber, I provide the ringing relay R, adapted to be set by a For purposes of listening in, and

- wire 8 and the return wire 9. This generator wire extends from the contact 'i of the commutator or interrupter I, to the thermal relay T, and thence to the contact 1? of the ringin relay R The return wire 9 on the other liand extends from the contact 1' of the ringing relay through the non-inductive resistance y to the ,main battery B and through the ground at g to the point 9 constituting the common connection of the battery B and the generator G to the commutator segments i and i is constantly driven while ringing, and may be maintained constantly in motlon, preferably by the same motor which drives the charging andringing machines. The driv- "ing means is immaterial to the present invention however, and may be anything'desirable or available ina particular case:

The ringing relay R has its windings connected on one side to the main battery B. On the other side they are connected through wire 11 to the key K and when that is closed to ground and so to the battery; and also through wire 12 to a self-locking device'consisting of the contacts r 'r?,' the latter connected through wire 13 to a contact 25 in the thermal relay T and thence through its normally closed mate t to ground. Whenever the key K is depressed for amoment, the relay R 'becpmes energized and upon pulling up its armatures locks itself on the followin lockin circuit B, R", 12, 1' 1', 13, t, t an roun This circuit however is controlled y the thermal relay, and the said thermal relay is controlled by the wanted subscriber,

40'-hav1ng one of its wires included in series with the ringing wire 8, so that when the subscriber answers the relaywill become energized to open its contacts t-t, breaking the locking circuit and. thereby deenergizing the ringing relay R, cutting off the ringing current and restoring the continuity of the cord circuit. The thermal relay is constructedv vand arranged in the following manner; a

tension y e t has attached to it but insulated from it the ends of two wires t and t 1 The other ends .of these wires are attached to.

' points on a pivoted lever t, these points lyingon opposite sides of the pivot 25 of the lever. The two wires are maintained under tension by means of the sprin i attached at one end to the yoke 25 andpat t e other to a fixed support t7. The lever t carries upon it a stud of insulation t, by which it can lift the contact spring t from its anvil t. Normally the spring rests on the anvil, and the wires t and t are maintained under uniform tension, so as to keep'the lever t in a neutral position. In order to multiply the movement of this lever, I mav make it of an len th desired.

The commutator Is;

in series with the relay wire i Generator current passing through the wire 8 must pass therefore through the relay wirealso, but the carrying capacity of the wire, and the amount of current which will assthrough the line wires and the ringer ol the'wanted subscriber are so ad'usted that such an amount of current wil not heat the relay wire sufiiciently to destroy the balance of relay obviously remains alanced, because both wires t and t are exposed tothe same changes, 4

In order to equalize the effects of the battery and generator currents. on the ther- 8o mal relay, I provide a capacity C in a shunt branch around the wire't This capacity or its equivalent means constitutes an important feature of my invention, a condenser eing employed which willshunt enough. of the alternatin current from the wire i to revent the latter being unduly heated. bince I intend that the thermal relay shall be 0 erated both by the battery current and by the ringing current, and since the voltage and consequently the relative amount of current flow thr,ough the same resistances is difierent for the ringing current and for the battery current, it is necessary to rovide some means for equalizing the eff cts of these currents on the thermal relay, and

I find the condenser or capacity afiects this very well. As a substitute forthis-condenser, Imay use a suitable resistance coil R as'showninFig. 11. f

The operation of my inventiorras thus far described will now be .understood.-' Al,- suming that subscriber A has called for connection with subscriber A ,and that the 0pswering 'ack J, has tested t e jack'J of the wanted inc and has inserted the plug 1? therein, it remains for her to a ply ringing current to the line 12 of su scriber A. This she does by depressing the key K'for 11 .a moment whereby the following circuit is closed: B, R, 11, K, and ground. Current in this circuit energizes relay R, which pulls up its armatures, opens the cord conductors 5-7 andjconnects the tip of the plug P to the commutator I through the following pathz'tip, to contact,'1' r, 8, i C in parallel, 8 to contact The relay also connects the sleeve of the plug through -the fol- The commutator I is supposed to-be rotating whereby its two segments i, 77 come into connection alternately with the spring it The segment i is shown as the larger of the "two, the period of ringing made longer'than the period of rest; butthis may be varied in any manner desired. The segment i is connected to the generator G, and thesegment i is connecteddirect to I have stated that the wire 8 is connected the relay. To all atmos heric effects the 75 v erator, has inserted the plu P into the an- 105' lowing path: sleeve, r211", 11, 9, B'andgroiinil.

thereby "being point g,-whence both branches are con'-.

- nected throughthe ground to the battery B. y The complete ringing circuit while generator is on is as follows z-G, ,218,153 and C in parallel, 8, 1', r tip, 3', 2, A, 1, j, sleeve, 1", 7', 1y, 9., B, ground, '9. and back to generator.

en thesegrnent 11 comes around'to the spring '71, the circuit is the same except/that t e generator is cut out andthe connection.

is completed from point 9 direct to the: ring 1,. This leaves the battery B alone in tie circuit, The relay R when pulling up also looked itself over the following circuit:

B, R, 12, r, 13, t, t and ground back to battery. I f a Figs. 3 and 4 show difl'erent arrangementsof the a paratus at the subscribers station.

It is to e observed that I am not confined I toany particular one of these arrangements, so long as the reqbuired basic feature is presente d, which is t .at with the line in a condition of disuse, a path of'relatively high resistance or low conductivity is closed for the generator or battery current upon. the line;

but when the subscriber takes down his re- .2

so adjuste that the amount of alternating ceiver for use, a path of relatively low resistance is close In Fig. 1 I have shown the subscriber's ringer permanently bridged across the line wit 1 a condenser interposed, the resistance of the ringer, either ohmic or inductive, or the capacit of the condenser, or both, being current which will ass in ringing is ihsuifi-- cient to heat the wire t of the thcrmic relay T to operate the latter. The condenser r'events the assage of direct current. W ien the subscribers tele hone is in use, a parallel path of relatively ow resistance is {closed through his talking set, which permits sufficient current, either-alternating brdirect,

to pass over the line, to heat the wire t so that its expansion will unbalance the relay '1, tilting the lever t .upon its pivot ti" so as to lift the spring t ofi theanvil t, to open the locking wire 13 thereby depriving the relay R of its ground, and permitting it to' retract so as to disconnect the wires 8 and 9 and reconnect thetip and sleeve of the plugI to the cord conductors 5 and 7 respectively. The arrangement shown in Fig. 2 is the same as that in Fig. 1 except that the ringer and condenser at the subscribersstation arenot permanently bridged but are disconnected when the telephone set is connected. The arrangement shown in Fig. 8 is similar in principle, but has the ringer, in a ground tap from the tip side of comes into use. With any of these arrangements it is suliiciently obvious that after thcopcrator has depressed the key ii and so energized the relay R, the latter Wlll remain lay is energized.

set of contact springs Z7, 7: am

locked until'the subscriber answers, when the thermic relay Twill release the relay It and stop the ringin I In Fig. 4 I have s iown amodified arrangement of the cord circuit, in which the wire 9 instead ofcbeing connected directly to the main battery B, is connected to a Wire 90 controlled by the relay B and receiving current from batteryonly when the said re- Thisarrangement has the advantage of leaving the signalingportions of the circuit. free from'- battery connections except when the calling plug is inserted in a spring jack. It should be noted that I leave the battery connected through the resistance y to the sleeve of the plug and thenc'through the thimble j" of the jack to the cut-oil relay N- during the ringing, the purpose of this being to maintain the cut-off relay constantly energized. This circuit may be traced as follows:- B, 9, y, 10, 1' 7, sleeve of P, j, N and ground. Also from P" through y' to line and back to' j, thence when ringing by Way of 1*, wire-8, t and commutator seginent to ground, either direct or through the generator. It should also be noted that thebattery current assists the generator current to operate the thcrmic relay when the subscriber answers, flowing out over the sleeve side of the line and back on the tip side and so through the wire 8' and through thegenerator'to ground. The relay R will be disconnected at the instant the subscriber answers, no matter what the position of the commutator I happens to be.

Fig. 5 shows my present invention ap ilied to aharrnonic ringing system, in which lifind an equalizing device such as the condenser C to be eminently desirable, if not necessary,

in order to secure a uniform. action of ringlug-current at d fferent frequencies upon the thermic relay. The arrangement and connections of the cord circuit andits bridging relaysare preferably the same in this case as those shown in Figs. 1 and 4., but as they are immaterial to the particular features important in harmonic ringing, they are not shown in Fig. 5. The plug P and the cord conductors 5 and 7,-with the ringing relay R, its arm atures, the battery wirc i), the rclay wire 10, the-resistance 3 the thermic rclay T, and the connecting wires 8 and 13 are al the same as in the foregoing description.

In the present case, howeven'the wire 1] instead oi passing to a single key K, uasses to a i k in parallel, these springs having anvilsic, 7c, 7c and 76 respectively, all connected in parallel through wire 14 to ground; Instead of a single generator G, there are four generators G", i", G and Gall connected on'ono side through the wire 15 to ground, and on the other side connected through the branch wires 16, 17, 1.8 and 19 to the corninutators I, l, I and I, respectively. From the con- Each unit key in this set has a cam roller conspread apart against their anvils and are so,

' springs-closed. A convenient form of'locksubscribers line 40-20 extending to four only- The ringers at these four stations are The line having been tested. and found idle,

' pushed-i all the way down so as to force both .the button is depressed, the pair of springs .ticular party, as the party at substation A, on

9, 10, R, 11, lrQ-k, 14', ground and back to tacts of these several commutators the wires 28, 38, 48 and 58 pass to the anvils 7c", 7c, k and 7c" of a set of selective rin ing buttons whose springs k, 7c, 7c and are connected in parallel to the wire 8. In Figs. 9 and 10 I have shown such a set of buttons.

nected to a push butt n stem so that when k, k, etc. with which it is'associated, are

maintained as long as the button is held down. Each button stem is rovided with a mechanical lock and all the uttons arein te'rlocking, the arrangement being such that when ressure is ap lied to one button, any other buttons which may have been down previously are at once released, and when pressure is removed from the button'in use, it retracts through a portion of its ath of movement so. as to open the groum spring 7c, 7r, but still. maintains the generator ing mechanism for such "a set of keys com-- prises thecommon latch shown extending along the side of the button stems, each stem having a pin or air of pins to engage said latch, these pins eing so; set that when any key is locked it is held with its generator contacts closed, and itsground contacts open. Other formsof locking mechanism and other arrangements of the springs will readily suggest themselves to those skilled in the art.

A form of cam and actuating button for an individual pair of springs is indicated in Fig. 5 in connection with the s rings k and k being marked 7:". It wi be understood that this is merely diagrammatic, but that if individual springs k, If, k and 7c are employed, there should be one of these double cams for each pair.

t, will be observed thatin Fig. 5 I show a substations A, A A andA, the st three of which are indicated by the ringer bridges tuned so that each will respond to a predetermined frequency of ringing current only. The four generators G, 'G2,'G3 andG", or the equivalent pole changers o'r'fre uency changers, arehrranged so as to supp y c.1 1r.' rent at corresponding frequencies.

Assuming that it is desired to ring a parthe line 4020,"the operation is as follows:

the plug P is inserted and the selective button associated with the springs 1:, k, is

its springs against the anvils k and 7c respecringing relay circuit is closed as follows: B,

battery. The ringing relay thereupon pulls its armatures and closes the circuit of the generator G to line as follows: G, 16, I, 28

7c, is, 8, t and C in parallel, 8, 1",, T to tip of plug P, line wire 10, all the substations, line wire 20, sleeve of plug P, 1", r, y, battery B, ground and wire 15 back to generator.

The ringers at substations A, A and A do not respond to current from generator G", but the ringer at substation A is effectively actuated, and continues to be so' actuated at intervals until the subscriber answers or until the plug P is withdrawn from his jack. In

the latter case, and assuming the cord -cir,-"

is removed therefrom, the spring 7: leaves from the contact 7c so .that the wire 11 is open, and the relay R is thereafter dependent upon its locking circuit 13. Further modifications of the arrangement in Fig. 5 may readily suggest themselves. As a further modification of the. arrangement in Fig.- 5, I ma use asingle commutator orinterrupter inserted in the wire 8 between the set of springs k, k, &c., and the thermic relay. The branches 16, 17, 18 and 19 will then go direct to the anvil contacts, 7c", k is and 7s", asshownin Fig. 12. 4

In Fig. 6 I have. shown the thermic relay T, the wires 8, 11 and 13 leadin to this relay and the keys, the ends of branc es 28, 38, 48

' and 58 and the key springs with their anvils,

the latter being arranged in series instead of in parallel, the object of this arrangement beingto prevent the connection of more than one generator to the-generator wire 8 at the \same time. When any generator spring is moved 'so as to make contact with its anvil,

'it is simultaneously disconnected from the following springs, so that'if two keys should besimultaneously pressed down, only the lowest one in order would connect lts generator to the wire 8. .2 In Fig. 7 have shown the four springs 7c, W, k and kreplaced-b-y a single master contact k which is closed on its anvil'lc 'when I ever. any of its individual. generator springs. 7c, k, k and k is closed and the button" thereof depressed to the fullest extent. The.

master contacts 74 and k are open at all other times. The same circuit and thesame key are indicated in Fig. 8 with the series arrangement of Fig-6. Unless some mechanicalmeans is provided to prevent the depression of two'buttons at the same time, by simultaneous pressure a cut-oil scheme of this kind iiiust be employed if it be desired-tag hooks The condenser action in of current at different frequencies prevent crossing of two frequencies. The ringing circuit being entirely automatic, if the operator should push down two'keys at once, two frequencies of ringing current would go to line until one of the subscribers answered.

The condenser Q in shunt with the wire t ot the therinic relay. is shown in all of the figures, constituting an essential feature of my invention. Its from this, that the therrnic relay, and in fact anyrelay-to operate satisfactorily in automatic ringing, must be provided'with some means to equalizethe effect thereon of cur-. rent at different frequencies. A uniform current flow must be maintained, and by means of this condenser shunt is maintained in the Wire i The condenser exhibits a lower resistance to the higher frequency currents and by properly determining the capacity in advance, the el'liciency of the shunt 18 made to vary approximately with the frequency. Thus, the same effect is produced in the thermic relay with a.higl'1 fre-'- qucncy current as with a low frequency. In some standard harmonic systems, the frequencles employed range from 16 to 66 cycles and the voltages are graded from 50, for the- 16 cycle current to 150 to 175 for the higher frequencies. If no shunt path were provided around the wire i of the thermic relay,

it would be impossible to adjust the sameso' as to allow the locking contact .t t" to remain closed wlth high freuency current flowing to line and with the te 'ephone receiver ,on the equalizing the effect is thus the same as ,in equalizing the alternating and direct current efiects, both these ellectsbeingcombined in harmonic ringing 5;!

.VVhile I have described my invention herein as applied through the agency of certain specificforms of apparatus, itis to be under-.,

stood'tliat these can be varied widcly'at will. I do not wish to limit myself toany' particular type of key, any particulartype of cord or line circuit, or any particular are rangemeatf of automatic or other rin ing. The resources of the art'are' varied an numerous and the field of choice in desi ning is ,a broad, one. I contem late app ying my invention to systems an apparatus of 7 various types and all such non-essential changes as are requlred to make It conform to any given system I desire'to have included within the scope of my claims. In its broadest aspect the feature of the condenser branch 0 is a ringing shunt or an equalizer, and I am fully aware that resistance or choking coils or other devices may be employed instead of a condenser for a similar purpose. It is to be understood, therefore, that in claiming an equalizer or balancing means,

I intend to include any means for producing importance will appear I and a uniform current and a uniform action in,

. the controlling device T.

Having thus described my invention what I claim and desire to secure by Letters Pat cut is- 1. In, a telephone exchangev system subs:

scribers lines and an operator's. cord circuit.

for interconnecting the same, with an. automatic ringing circuit therefor comprising the following instrumenta'lities a. ringing relay adapted to open thecord and connect the calling plug to a generator wire, alternating and direct; current sources, and a-commutator acting; to connect the same alternately to the generator wire and thenceto the sub scribers line through the ringing relay, to;

getherwith a thermal relay connected tothe generator wire and controlling the ringing; relay, and equalizing ineansassociated with,

said thermal relay, substantially as described.

2. In a telephone'exchange system, subscribers lines and an operators cord circuit for interconnecting the same, with an automatic ringing circuit therefor comprising the following instrumentalities: a ring ng relay adapted to open the cord andiconnect the and 'rect current sources, and a commutator acting to connect the same alternately to the generator wire 'and thence to the sub scribers line through'the ringingrelay, 'togetherwith a balanced thermal relay connected on one side to the enerator wire and calhn plug to a generator wire, alternating V controlling the ringing relay, and anequalizing shuntfor the thermal relay, substantially-as described. 1

3; In a telephone exchange system, subscribers lines and an operators cord circuit tator acting to connect the same alternately to the generatorwire and thence to the sub -scribers line through-the ringing relay, to-

gether with a balanced thermal relaycon nected on one side to the generator wire andcontrolling the ringing relay, and "a capacity in shuntof said thermal relay;

4. In a telephone-exchangesystem, subscribers lines and an operators cord circuit for interconnecting the same, with an automatic ringing clrcuit therefor comprlsing the following instrumentalities: a ringing relay adapted to open the cord and connect the callm plug to a generator wire, alternating and irect current sources, and a commutator acting to connect the same alternately to the generator wire and thence to the sub-. scribers line through the ringing relay, together with abalanced thermal relay con- ,nected on one side of said generator wire and controlling said ringing relay, and a condenser in shunt of that portion of the thermal relay which is connected to thegenerator.

wire, substantially as described.

5. In a telephone exchange system, automatic ringing means comprising a suitable generator of ringing current, and a noninductive controlling relay with an equalizing shunt, in the generator circuit, substantially as described. 1

j 6. In a telephone exchange system, an automatic ringing scheme comprising a generator of ringing current, anda thermal controlling relay therefor-connected in the generator circuit, with an equalizing shunt,

substantially as described.

7. in a telephone exchange system, automatic ring ng means comprising a generator circuit, means for connecting the same to a wanted line, a controlling device therefor and an equalizing shunt for the said controlling device adapted to produce a substantially uniform current and uniform action therein, substantially as described.

8. In a telephone exchange system, automatic ringing means comprising a generator of ringing current, means for connecting the same to a wanted line, and a thermal controlling relayv therefor with a condenser in shunt thereof, said relay being responsive to current in the generator circuit as deter ,mined by the act of the subscriber, substan-.

means controlled by current in the wanted subscribers line and itself controlling the generator circuit, and an equalizing shunt for said controlling means, substantially as described.

' 11. In a telephone exchange system, the combination of a ringing generator, a direct current generator, a generator wire, a commutator for connecting the generators'to said wire alternately, a ringing key for connecting the generator wire to a, wanted line, a thermal device having a pair of.wires equally exposed to atmospheric changes but one only connected in series with the generator wire, and a condenser in shunt therewith to equalize the eilects of the different currents 11ow- .ing therethrough, substantially as described.

12. In a telephone exchange system, a ringing generator, a ringing circuit from such generator to line, a non-inductive controlling relay connectedto such circuit and adapted to be operated by current flowing therethrough, and a shunt about such relay for equalizing the flow of current therethrough. 13. 111 a telephone exchange system, an alternating current ringing generator, a ringing circuit extending therefrom to line, a noninductive controlling relay connected to such circuit, and a shunt around such relay, such shunt offering a difl'erent resistance to alternating currents of difl'erent frequencies,

14. In a telephone exchange system, an

alternating current ringing generator, at circult from such generator to line, a noninductive 'controlhng relay connected to such circuit, and a shunt around such relay, such shunt adapted to regulate the ilow of current through the relay for variations in the frequency of such current.

In testimony whereof I afiix my signature inpres nce of two witnesses.

RAY H. MANSON Witnesses A. J. ltonnn'rs, W. C. STRONG. 

